1. Field of the Invention
An apparatus consistent with the present invention relates to an inspection system for RFID tags and, more specifically, to an inspection system which determines the communication performance of RFID tags, based on how much their resonant frequencies are shifted from a target value.
2. Description of the Related Art
In recent years, RFID (radio frequency identification) tags have been widely used in distribution systems and entering and leaving control systems, etc. An RFID tag has a memory in its integrated circuit (IC). This memory responds data from a reader/writer and, then transmits/receives data to or from the reader/writer in a non-contact manner. This transmission/reception is performed through respective coiled antennas provided in both an RFID tag and a reader/writer. Hereinafter, the coiled antenna of the RFID tag is referred to as “tag antenna”, and the coiled antenna of the reader/writer is referred to as “reader/writer antenna”. A reader/writer energizes an RFID tag and, simultaneously transmits/receives data to or from the RFID tag through their antennas by means of electromagnetic induction. As a result, a non-contact data transmission/reception between the RFID tag and the reader/writer is established.
Such RFID tags are attached to packages of food products and of industrial products for the purpose of controlling their production or distribution process. In addition, RFID tags are contained in cards, thereby constituting prepaid cards.
On the other hand, manufacturers of products equipped with an RFID tag need to inspect the functions of the RFID tags before and after the attachment to the products or their packages. Typically, this inspection is represented by a data communication test between an RFID tag and a reader/writer. An example of this test method is described in Japanese Unexamined Patent Application No. 2002-230510.
This test method makes it possible to determine whether or not RFID tags operate successfully, but does not yet determine the cause of the abnormalities of RFID tags if any abnormalities are detected. In other words, an abnormality of RFID tags is caused mainly by the failure of their IC chip, the contact failure between their IC chip and tag antenna, or the lack of the property of their tag antenna. However, with the above test method alone, which of these three causes cannot be identified.
An object of the present invention is to provide an RFID tag inspection system which inspects the properties of tag antennas, and further, which determines the communication performance of RFID tags, based on how much their resonant frequencies are shifted from a target value.